a) Field of the Invention
This invention relates to a knowledge-based system for generating a holistic health index for diagnosis and decision support in operational management of biological treatment of waste water with a microbial population; to a method of generating such a holistic health index; and to a method for managing a biological treatment of waste water with a microbial population. The invention has particular application in the treatment of waste water from a pulp and paper mill.
b) Description of Prior Art
Waste water treatment is generally classified as primary or secondary treatment. Primary treatment usually involves a mechanical process to remove sediments and clarifiable solids from the influent and to condition the waste water for secondary treatment. Secondary treatment mainly relies on biological processes to reduce biological oxygen demand (BOD) and certain toxicity in waste water to an acceptable level before it is discharged to the environment. In some industries, effluents from secondary treatment may require further chemical treatment to remove specific toxic materials before discharge.
Microbial activities are the essential component of secondary treatment. The microorganisms function as a biological system with their living environment. The waste water is usually aerated to provide dissolved oxygen to support microbial growth. The microorganisms populate and consume the organic wastes in the waste water. The biological treatment process produces biomass or sludge that has to be removed from the treatment tank. The sludge may promote or hinder the desirable microbial activities depending on its amount in the treatment tank. Treatment is optimal if a delicate balance of sludge is maintained with respect to the input conditions of the influent and other operating parameters.
Because the treatment is biological in nature, influent and other operational conditions directly affect the microbial activities and subsequently the performance of the treatment process. If the microbial living environment favours the desirable microbial activities, good performance is achieved, and vice versa. In extreme cases, the entire microbial population may die as a result of shock or toxicity. Shock may come from excessive input conditions in the influent and from the changing open environment. Toxicity may be present in the influent or it could be self-induced by some microbial activities in certain situations. The microbial population can also be overpopulated by unwanted microorganisms that deteriorate treatment. Recovery time is usually long once the desirable microbial population is gone.
In the case of waste water from a pulp and paper mill compliance with strict environmental regulations may require the mill to shut down its production or reduce its production capacity during the long recovery period when the biological treatment is not proceeding adequately. There is undoubtedly high corporate interest in avoiding costly production loss.
There are at present no easy tools available to field operators to prevent microbial disasters from happening. Prior practice does not provide a comprehensive and holistic measure of the health of the microbial population in the treatment tank as an organic living system in its own right, with respect to its function in the treatment process. Standard field measurements typically focus on monitoring influent and effluent parameters. More sophisticated measurements in areas of floc morphology and identification of specific groups of microorganisms, floc settlability, microbial activity and nutrient balance are all stand-alone approaches. It requires considerable knowledge and experience of a trained person to make an integrated diagnostic comprehension. The field operator can observe operational symptoms when the illness has advanced into an observable operational stage. In many instances it is already too late to avoid any loss in mill production. Field operators generally are not trained to have the knowledge or the specialized skills to conduct a microbial diagnosis of the illness symptoms or to prevent microbial disasters from happening in the first place.